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Instructor's Manual and Test Bank to accompany Meteorology Today, 10th Edition
Jonathan D. W. Kahl
University of Wisconsin-Milwaukee
Chapter 15
Hurricanes
Summary
Tropical weather and hurricanes are discussed in this chapter. Several unusually strong and
destructive hurricanes have affected the US in the past several years and this subject should be especially
relevant and interesting to students.
The chapter begins by examining how hurricanes, intense tropical storms with a structure
markedly different than that of a middle-latitude cyclone, form and disspiate. Schematic diagrams of the
air motions in a mature hurricane and characteristic hurricane features including the eye, eye wall and
spiral bands, are given. The differences between hurricanes and middle latitude storms are highlighted in
a focus section.
The special conditions that make it possible for a mass of thunderstorms to become organized and
develop into or 'trigger' a tropical storm or hurricane are examined in detail. Hurricanes form above and
derive much of their energy from a warm surface layer of ocean water. Horizontal temperature and
pressure gradients are weaker in the tropics, for example, than at middle latitudes. Moisture is abundant
in the tropics, however, and zones of convergence such as might be found associated with an easterly
moving wave or near the ITCZ can cause thunderstorms to form. Hurricanes generally form between 5
and 20 degrees latitude, where steering winds will cause an overall east to west movement.
Some of the unique hazards associated with hurricanes are discussed. In addition to powerful
winds and flooding caused by heavy rainfall, extensive damage can be caused by the hurricane storm
surge. Several particularly noteworthy hurricanes are described in detail, including a focus section on
“The Record-Setting Hurricane Seasons of 2004 and 2005”.
The following section on hurricane forecasting reveals that forecasting when and where
hurricanes will form remains an inexact science. A focus section on “Hurricanes in a Warmer World”
describes the possible relationships between global warming and the frequency and intensity of
hurricanes.
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Teaching Suggestions
1.
Video footage of recent hurricanes is available from the National Hurricane Center,
www.nhc.noaa.gov.
2.
Using realtime weather images, compare the size, wind speed, and precipitation patterns between
a middle latitude cyclone and a tropical storm. Discuss similarities and differences.
3.
Examine realtime sea surface temperatures to see if current conditions are ripe for tropical storm
formation:
http://www.ssd.noaa.gov/PS/TROP/DATA/RT/sst-atl-loop.html
4.
Examine the National Hurricane Center’s Historical Hurricane Tracks website to see the history
of hurricane passage near your area:
http://www.csc.noaa.gov/hurricanes/#
5.
Overlay Figure 15.32 with a map showing cities along the projected hurricane paths. Conduct a
discussion as to whether cities along the paths should be evacuated.
6.
Examine current global satellite imagery for tropical storms.
7.
Discuss the potential role of western African dust storms on Atlantic hurricanes. More dust in the
atmosphere could lead to reduced solar radiation, reduced sea surface temperatures and fewer/weaker
tropical storms.
8.
Review the National Hurricane Center advisories for the devastating 2005 Hurricane Katrina with
the class. Discuss the impact of these advisories.
http://www.nhc.noaa.gov/archive/2005/KATRINA.shtml
9.
Invite students to report on any personal experiences they may have had with tropical storms.
10.
Have students discuss the merits of hurricane modification. This could be a lively discussion.
Student Projects
1.
Depending on the time of the year students may be interested in plotting and following hurricane
or tropical storm trajectories on a tracking chart. Students can investigate how large, synoptic-scale
weather features affect the storm's movement.
2.
Have students prepare a report on a strong recent hurricane (a suitable choice could be made from
the list of retired names in the text) or a hurricane of historical interest. Detailed information is available
at the National Hurricane Center’s data archive site:
http://www.nhc.noaa.gov/pastall.shtml
3.
Have students debate the merits of evacuating town residents when the probability of a hurricane
strike is 20%, 40% and 60%.
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4.
Have students read Dr. Jeff Masters’ fascinating account of flying through the eyewall of
Hurricane Hugo:
http://www.wunderground.com/resources/education/hugo1.asp
5.
Have students interview a city planner in a hurricane-prone region to learn about that city’s
procedures when threatened by tropical storms.
Answers to Questions for Review
1.
A weak trough of low pressure in the tropics. They generally travel from east to west. On the
eastern side, where the southeasterly winds converge, rising air generates showers and thunderstorms.
2.
Streamlines are useful because they show where surface air converges and diverges.
3.
Typhoon.
4.
Horizontal structure: As one approaches the hurricane, the sky becomes overcast with cirrostratus
clouds; barometric pressure drops slowly at first, then more rapidly as we move closer to the center.
Winds blow from the north and northwest with ever-increasing speed as we near the eye. The high winds,
which generate huge waves over 10 m (33 ft) high, are accompanied by heavy rainshowers. As we move
into the eye, the winds slacken, rainfall ceases, and the sky brightens, as middle and high clouds appear
overhead. Vertical structure: Near the surface, moist tropical air flows in toward the hurricane’s center.
Adjacent to the eye, this air rises and condenses into huge cumulonimbus clouds that produce heavy
rainfall, as much as 25 cm (10 in.) per hour. Near the top of the clouds, the relatively dry air, having lost
much of its moisture, begins to flow outward away from the center. This diverging air aloft actually
produces an anticyclonic (clockwise in the Northern Hemisphere) flow of air several hundred kilometers
from the eye.
5.
Air is sinking in the eye, causing adiabatic warming and preventing cloud development.
6.
Hurricanes form over tropical waters where the surface winds are light, the humidity is high in a
deep layer extending up through the troposphere, and the surface water temperature is warm, typically
26.5°C (80°F) or greater, over a vast area. Aloft, the trade wind inversion must be weak and upper-level
winds must not be strong.
7.
Convergence of winds along the ITCZ; formation of a low pressure area along a wave in the
ITCZ; convergence along the eastern size of an easterly wave; convergence along a midlatitude front that
has moved into the tropics.
8.
a. Water vapor evaporating from the ocean surface. b. The maximum strength a hurricane can
achieve is proportional to the difference in air temperature between the tropopause and the surface, and to
the potential for evaporation from the sea surface.
9.
No, because the energy supply (evaporation of large amounts of surface water) is unavailable.
10.
Northern side; eastern side.
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11.
land.
Wind shear, passage over cooler or shallower water, increased ocean wave activity, passage over
12.
Initially, the mass of thunderstorms with only a slight wind circulation is known as a tropical
disturbance, or tropical wave. The tropical disturbance becomes a tropical depression when the winds
increase to between 20 and 34 knots and several closed isobars appear about its center on a surface
weather map. When the isobars are packed together and the winds are between 35 and 64 knots, the
tropical depression becomes a tropical storm. The tropical storm is classified as a hurricane only when its
winds exceed 64 knots (74 mi/hr).
13.
Similarities: both have central cores of low pressure and winds that spiral counterclockwise about
their respective centers (Northern Hemisphere). Differences: A hurricane derives its energy from the
warm water and the latent heat of condensation, whereas the midlatitude storm derives its energy from
horizontal temperature contrasts. The vertical structure of a hurricane is such that its central column of air
is warm from the surface upward; consequently, hurricanes are called warmcore lows. A hurricane
weakens with height, and the area of low pressure at the surface may actually become an area of high
pressure above 12 km (40,000 ft). Mid-latitude cyclones, on the other hand, are cold-core lows that
usually intensify with increasing height, with a cold upper-level low or trough often existing above, or to
the west of the surface low. A hurricane usually contains an eye where the air is sinking, while midlatitude cyclones are characterized by centers of rising air. Hurricane winds are strongest near the surface,
whereas the strongest winds of the mid-latitude storm are found aloft in the jet stream.
14.
Steering winds in the tropics are usually easterly.
15.
The huge waves and flooding associated with the storm surge usually cause the most destruction.
16.
Flooding.
17.
The combined effect of high water (which is usually well above the high-tide level), high winds,
and the net Ekman transport toward the coast, produces the storm surge—an abnormal rise of several
meters in the ocean level—which inundates low-lying areas and turns beachfront homes into piles of
splinters. The storm surge is particularly damaging when it coincides with normal high tides.
18.
The name is assigned when the storm reaches tropical storm strength.
19.
Spin-up vortices (mini-swirls).
20.
Katrina’s rainbands near the center of the storm converged, cutting off moisture to the eyewall
and causing it to dissipate. A new one formed farther away.
21.
Information from satellites, buoys and data collected by reconnaissance aircraft are fed into
computer models, which forecast the movement and intensity of the storm.
22.
When a hurricane poses a direct threat to an area, a hurricane watch is issued. When it appears
that the storm will strike an area within 24 hours, a hurricane warning is issued.
23.
In attempts to reduce their winds.
24.
Sea surface temperatures offshore of New Jersey are warmer than those offshore of Oregon.
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Also, a typical path of Atlantic Hurricanes passes westward across the Atlantic toward the Caribbean Sea,
then turns northward along the eastern shore of North America, passing close to New Jersey. Typical
paths of Pacific hurricanes pass nowhere near Oregon.
Answers to Questions for Thought
1.
In May the surface ocean water in the subtropics is still relatively cool from the winter. In
October the water is still warm from the summer.
2.
It would be possible if the water temperature remained warm enough. During most years the
water is too cold to generate hurricanes and so the hurricane season officially ends on November 30.
However, during a strong El Niño event, the water may remain warm into December. As an example,
Hurricane Winnie formed over the tropical eastern Pacific on December 4, 1983.
3.
The winds would decrease more quickly when the hurricane moves over land. The storm would
be deprived of its primary source of energy (latent heat of condensation) and friction with the surface
would disrupt its circulation and slow its winds.
4.
The rapid rate of evaporation cools the water.
5.
Veering to the south of the storm. The hurricane's strongest winds would be found in its northern
sector.
6.
It would not necessarily begin with the letter C because several tropical storms may have formed
but not developed into full-blown hurricanes before this.
7.
To the east. Winds circulate clockwise around tropical cyclones in the Southern Hemisphere, so
the onshore winds (and the storm surge) will arrive to the east of Darwin.
8.
The hurricane’s dissipation will be somewhat slowed if it encounters a mountain range after
making landfall, because orographic lifting will provide some vertical motions to the air. The most
damage is likely to be from flooding and flash flooding resulting from heavy rains.
9.
Possible reasons include: the hurricane can pass over an area of warm surface ocean water, it can
move away from the equator where the Coriolis force is stronger, it can experience decreasing levels of
vertical wind shear, the trade wind inversion can weaken, upper-level divergence can increase.
10.
Yes. The tropical storm should be given a new name because it is now an eastern Pacific storm,
which are named according to a different list than north Atlantic storms.
Answers to Critical Thinking Questions
Figure 15.1.
Yes, in the region of the southern hemisphere trade winds. The rain would still be
expected to be on the wave’s eastern side, in the area of convergence.
Figure 15.27. From the north. Ekman transport would be toward the west, putting a great strain on the
levees of New Orleans.
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Multiple Choice Exam Questions
1.
Streamlines on a weather map depict
a. water temperature.
b. pressure.
c. wind flow.
d. dew point.
e. ocean currents.
ANSWER: C
2.
Which of the following is not true concerning an easterly wave?
a. moves from east to west
b. has converging winds on its western side
c. showers and thunderstorms may be found on its eastern side
d. indicates a region of lower-than-average pressure
ANSWER: B
3.
Suppose the eye of a hurricane passed directly over you, and you survived the experience. If
winds were from the northeast as the eyewall first approached you, from what direction did the winds
blow when the eyewall reached you the second time?
a. NW
b. NE
c. SE
d. SW
ANSWER: D
4.
Pressure at the center of a hurricane is ____ than the surroundings at the surface and ____ than
the surroundings aloft.
a. higher, lower
b. lower, higher
c. lower, lower
d. higher, higher
ANSWER: B
5.
The vertical structure of the hurricane shows an upper-level ____ of air, and a surface ____ of air.
a. outflow, inflow
b. outflow, outflow
c. inflow, outflow
d. inflow, inflow
ANSWER: A
6.
In the Northern Hemisphere, hurricanes and middle latitude cyclones are similar in that both
a. have surface weather fronts.
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b. intensify with increasing height above the ground.
c. have winds that blow counterclockwise around their centers.
d. will generally move from west to east.
ANSWER: C
7.
Which would you not expect to observe as the eye of a hurricane passes directly over your area?
a. an increase in surface temperature
b. a very low surface pressure reading
c. high winds
d. little or no precipitation
ANSWER: C
8.
Most hurricanes have fronts.
a. true
b. false
ANSWER: B
9.
In a hurricane, the eye wall represents
a. the exact center of the storm.
b. the area of broken cloudiness at the center.
c. a region of light winds and low pressure.
d. a zone of intense thunderstorms around the center.
e. a layer of cirrus cloud in the center of the storm.
ANSWER: D
10.
The strongest winds in a hurricane are found
a. at the center of the storm.
b. in the eye wall.
c. in the rain bands.
d. at upper levels, above the center of the hurricane.
e. near the periphery of the hurricane.
ANSWER: B
11.
Hurricane winds rotate in a clockwise direction
a. in the Northern Hemisphere only.
b. in the Southern Hemisphere only.
c. in both the Northern and Southern Hemispheres.
d. in neither hemisphere.
ANSWER: B
12.
At the periphery of a hurricane, the air is ____, and several kilometers above the surface, in the
eye, the air is ____.
a. sinking, sinking
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b. sinking, rising
c. rising, sinking
d. rising, rising
ANSWER: A
13.
In order for a hurricane to form, the layer of warm water must extend from the ocean surface to a
depth of at least 400 meters.
a. true
b. false
ANSWER: B
14.
As a northward-moving hurricane passes to the east of an area, surface winds should change from
a. NW to N to NE.
b. W to SW to S.
c. NE to N to NW.
d. S to SW to W.
e. SE to S to SW.
ANSWER: C
15.
The main reason hurricanes don't develop over the South Atlantic Ocean adjacent to South
America is because
a. the Coriolis force is too small there.
b. the pressure gradient force is too weak in that area.
c. the surface water temperatures are too cold.
d. the air at the surface is always diverging.
ANSWER: C
16.
Hurricanes do not form
a. along the ITCZ.
b. along the equator.
c. with an easterly wave.
d. when the trade wind inversion is weak.
e.
ANSWER: B
17.
As surface air rushes in toward the eye of a hurricane, the air expands and should cool. The main
reason the surface air is not cooler around the eye is because
a. the sinking air near the eye warms the air.
b. friction with the water adds heat to the air.
c. the warm water heats the air.
d. sunlight heats the air.
ANSWER: C
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18.
The main source of energy for a hurricane is the
a. upper-level jet stream.
b. rising of warm air and sinking of cold air in the vicinity of weather fronts.
c. warm ocean water and release of latent heat of condensation.
d. ocean currents and tides.
ANSWER: C
19.
Which below only forms over water?
a. thunderstorms
b. funnel clouds
c. tornadoes
d. mesocyclones
e. hurricanes
ANSWER: E
20.
Hurricanes dissipate when
a. they move over colder water.
b. they move over land.
c. surface inflow of air exceeds upper-level outflow of air.
d. all of these
ANSWER: D
21.
Which is not an atmospheric condition conducive to the formation of hurricanes?
a. a region of converging surface winds at the surface
b. warm water
c. strong upper-level winds
d. cold air aloft
e. moist, humid surface air
ANSWER: C
22.
Just before a storm becomes a fully developed hurricane, it is in the ____ stage.
a. tropical depression
b. tropical disturbance
c. tropical storm
d. cyclone
e. typhoon
ANSWER: C
23.
The main difference between a hurricane and a tropical storm is that
a. hurricanes are larger.
b. tropical storms are more than 500 miles from the U.S. mainland.
c. winds speeds are greater in a hurricane.
d. hurricanes have a clearly defined eye on satellite photographs.
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ANSWER: C
24.
The first three stages of a developing hurricane are (from first stage to third stage)
a. tropical disturbance, tropical storm, and typhoon.
b. tropical depression, tropical disturbance, and tropical storm.
c. tropical disturbance, tropical depression, and tropical storm.
d. cyclone, typhoon, and tropical storm.
ANSWER: C
25.
Which statement below is not correct concerning hurricanes?
a. They may contain tornadoes.
b. They may contain severe thunderstorms.
c. A hurricane moving northward over the Pacific will normally survive for a longer time
than one moving north over the Atlantic.
d. A weakening hurricane can move up to middle latitudes and turn into an extratropical
cyclone.
ANSWER: C
26.
Which method below describes how scientists have tried to modify hurricanes?
a. putting an oil slick over the ocean water and igniting it
b. seeding the hurricanes with silver iodide
c. igniting huge smoke bombs in the eye of the storm
d. seeding the hurricanes with hair-thin pieces of aluminum called chaff
ANSWER: B
27.
Which of the following areas in the United States would most likely experience thunderstorms,
hurricanes, and tornadoes during the course of one year?
a. Pacific Coast states
b. New England states
c. Gulf Coast states
d. Great Plains states
ANSWER: C
28.
On the Saffir-Simpson scale, a category 5 storm would indicate
a. a weak hurricane.
b. a moderately strong hurricane.
c. a very strong hurricane.
d. None of these; the Saffir-Simpson scale applies to tornadoes.
ANSWER: C
29.
Which below is the best indication that a hurricane will likely strike your area within 24 hours?
a. a hurricane watch issued by the National Weather Service
b. high cirrus clouds moving in from the east
c. a hurricane warning issued by the National Weather Service
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d. easterly or northeasterly winds with speeds in excess of 30 knots
e. a rapid drop in pressure and heavy rains
ANSWER: C
30.
The strongest winds in a hurricane heading westward toward Florida would most likely be found
on the ____ side.
a. northern
b. southern
c. eastern
d. western
ANSWER: A
31.
Most of the destruction caused by a hurricane is due to
a. high winds.
b. flooding.
c. tornadoes.
d. hail.
ANSWER: B
32.
A strong trade wind inversion ____ to the development of a hurricane.
a. is conducive
b. is not conducive
c. is immaterial
ANSWER: B
33.
A hurricane warning
a. gives the exact location where a hurricane will make landfall.
b. is usually issued several days ahead of a hurricane's arrival.
c. gives the percent chance of a hurricane's center passing within 65 miles of a community.
d. is issued when a hurricane approaches to within 500 miles of the U.S. mainland.
e. is issued whenever surface wind speeds exceed 74 mi/hr.
ANSWER: C
34.
A storm of tropical origin whose high winds and water cause a great deal of destruction to islands
in the western North Pacific is (in this part of the world) known as a
a. hurricane.
b. cyclone.
c. willy willy.
d. mesocyclone.
e. typhoon.
ANSWER: E
35.
An intense storm of tropical origin that forms over the Pacific Ocean adjacent to the west coast of
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Mexico would be called a
a. hurricane.
b. typhoon.
c. cyclone.
d. willy willy.
e. baguio.
ANSWER: A
36.
Which of the following is true?
a. Hurricanes are only given male names.
b. Hurricanes are only given female names.
c. Hurricanes are alternately assigned male and female names.
d. Atlantic hurricanes are given male names and Pacific hurricanes are given female names.
ANSWER: C
37.
Suppose that five of this year's tropical storms develop into hurricanes over the North Atlantic
Ocean. The name of the third hurricane would start with the letter
a. A.
b. B.
c. C.
d. D.
e. impossible to tell
ANSWER: E
38.
Storms that form in the tropics are given names when
a. they reach tropical storm strength.
b. they become fully developed hurricanes.
c. they approach to within 250 miles of land.
d. rotation becomes visible on a satellite photograph.
ANSWER: A
39.
Hurricanes can't form along the equator because
a. there isn't much water along the equator, it's mostly land.
b. the Coriolis force is too small along the equator.
c. there are no feedback mechanisms along the equator.
d. it's too humid for the ocean water to evaporate.
ANSWER: B
40.
The energy for hurricanes comes from the transfer of ____ from the ocean surface to the
atmosphere.
a. sensible heat and momentum
b. latent heat and momentum
c. infrared radiation and momentum
d. sensible heat and latent heat
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ANSWER: D
41.
The favorable stability condition for hurricane development is
a. a deep layer of stable air.
b. a shallow layer of absolutely unstable air.
c. a shallow layer of conditionally unstable air.
d. a deep layer of conditionally unstable air.
ANSWER: D
42.
Hurricanes have strong divergence at their tops.
a. true
b. false
ANSWER: A
43.
Because of the conservation of angular momentum, air spiraling inward toward the center of a
hurricane ____ in speed.
a. decreases
b. increases
c. remains constant
ANSWER: B
44.
The immense amounts of energy taken in by hurricanes are
a. converted to kinetic energy.
b. used in chemical reactions.
c. lost through radiational cooling at the top of the storm.
d. converted to kinetic energy and lost through radiational cooling at the top of the storm.
ANSWER: D
45.
As latent heat is released inside the clouds of a hurricane, the warming of the air aloft creates an
area of ____ aloft.
a. low pressure
b. high pressure
ANSWER: B
46.
Surface winds in hurricanes typically reach a maximum in the
a. eye.
b. eyewall.
c. anvils.
ANSWER: B
47.
There is a limit to the intensity of hurricanes.
a. true
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b. false
ANSWER: A
48.
The process by which a hurricane's innermost ring of clouds dissipates and then strengthens is
called
a. landfall.
b. storm surge.
c. eyewall replacement.
d. spiral rainbands.
ANSWER: C
49.
The most costly hurricane ever to hit the United States was
a. Hurricane Ivan.
b. Hurricane Katrina.
c. Hurricane Wilma.
ANSWER: B
50.
Computer models of hurricanes almost always agree on their predictions of a hurricane's
movement and evolution.
a. true
b. false
ANSWER: B
Essay Exam Questions
1.
In what ways are weather conditions in the tropics and at middle latitudes different?
2.
Why can’t hurricanes form in the mid-latitudes?
3.
Very heavy rainfall amounts are often recorded when a hurricane or tropical storm moves over
land. Why do these storms produce so much rain?
4.
List and describe some of the conditions that are favorable to hurricane development. What
atmospheric conditions inhibit hurricane formation and growth?
5.
Would you expect hurricanes in the Southern Hemisphere to be any different from hurricanes in
the Northern Hemisphere? Why or why not?
6.
Hurricane season for the tropical North Atlantic and North Pacific oceans normally runs from
June through November. Why don't hurricanes form in these locations at other times of the year?
7.
Describe a hurricane as completely as you can by giving typical values for the following
characteristics: diameter, location and size of the eye, direction of rotation and speed of winds,
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central pressure, direction and speed of movement, duration.
8.
Where is the Bermuda high located during the summer and fall? How might the path of a
hurricane, moving toward the west from Africa, be affected by the Bermuda High as the
hurricane approaches the United States?
9.
Compare the size of an average hurricane to that of an average tornado. Given the size and
intensity of each, which do you think is the more destructive storm? Why?
10.
In your opinion do hurricanes pose the greatest threat to the east or west coast of the United
States? Explain.
11.
Even though more hurricanes form, on average, over the Eastern Pacific than over the tropical
North Atlantic, we generally hear less about them. Why do you think this is so?
12.
In recent years, the number of deaths caused by hurricanes has decreased, but the cost of
hurricane damage has increased. How would you explain this?
13.
What is a storm surge? How does a storm surge form?
14.
Compare and contrast the main features of a hurricane with those of a strong mid-latitude
cyclone.
15.
Why are the measurements made by reconnaissance aircraft so important to forecasting a
hurricane’s movement?